Add flag to launch two displays for mus+ash.

services/ui/ws/frame_generator_delegate.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_
 #define SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_
 
 #include "base/macros.h"
 
 namespace ui {
 namespace ws {
 
 class ServerWindow;
 
 struct ViewportMetrics {
-  gfx::Size size_in_pixels;
+  gfx::Rect bounds;
   float device_scale_factor = 0.f;
 };
 
 class FrameGeneratorDelegate {
  public:
   // Returns the root window of the display.
   virtual ServerWindow* GetRootWindow() = 0;
 
   // Called when a compositor frame is finished drawing.
   virtual void OnCompositorFrameDrawn() = 0;
 
   virtual bool IsInHighContrastMode() = 0;
 
   virtual const ViewportMetrics& GetViewportMetrics() = 0;
 
  protected:
   virtual ~FrameGeneratorDelegate() {}
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_FRAME_GENERATOR_DELEGATE_H_